The present invention relates to stoves of the space heater variety and/or stoves which may be used as a furnace. In most cases the fuel used for such stoves is wood, although other fuels, such as coal, for example, may be used. Although not limited thereto, the present invention relates primarily to wood burning stoves of the airtight variety.
In recent years, due primarily to the energy crisis, wood burning stoves have enjoyed an ever-increasing popularity and public acceptance. The ultimate objective in stoves of this type is to achieve as complete combustion as possible of the combustion gases, since with more efficient combustion, burn time can be increased because it is possible to slow the fire down and still obtain the desired heat transfer for maximum comfort. However, most existing stoves of this type, i.e. airtight wood burning stoves, have a combustion efficiency somewhere in the range of fifty to sixty percent, primarily due to the fact that the ignition point of combustion gases is in the general range of 1300.degree. F. whereas the temperatures generated in stoves of this type are usually in the range of 500.degree. to 900.degree. F. Thus, efficient combustion of these combustion gases has been difficult, if not impossible, to achieve, resulting in lower combustion efficiency, which in turn results in creosote build-up in the chimney or flue, which build-up frequently results in chimney fires. Also, reduced combustion efficiency results in undesirable smoke pollution.
The concept of using a catalytic converter in stoves of this type to obtain greatly increased combustion efficiency is not new and is disclosed, for example, in co-pending U.S. application Ser. No. 195,399, filed Oct. 9, 1980, entitled "Stove Construction". Specifically, by causing the combustion gases to flow through a catalytic converter before reaching the exhaust duct or flue of the stove, the ignition point of the escaping combustion gases is lowered to the general range of 500.degree. F., thus resulting in almost complete afterburn of these gases in the normal range of operating temperatures in stoves of this type. This results in combustion efficiency in the general range of ninety percent, or in other words, an efficiency of approximately thirty-five percent more than that achieved by traditional airtight wood burning stoves. This increased efficiency means little or no pollution will enter the atmosphere because the smoke, a normal by-product of conventional wood stoves, is virtually eliminated, leaving a harmless humid vapor in its place. In addition, as a result of the almost perfect combustion that takes place, there is virtually no creosote build-up in the chimney, thus greatly reducing chimney fire hazards and at the same time reducing chimney maintenance. Furthermore, peak performance can be obtained even with the use of soft and unseasoned wood and burn time can be increased because it is possible to slow the fire down and still maintain almost perfect combustion while transferring heat temperatures necessary for maximum comfort.
The present invention is also directed to the use of catalytic converters in wood stoves, and like the aforesaid co-pending Schwartz application, it is desired to have all of the combustion gases pass through the catalytic converter when the stove is in its normal operating mode. However, since the catalytic converter is in the nature of a filter which to some degree resists or impedes the flow of combustion gases therethrough, it will be apparent that when the access door of the stove is open, the combustion gases and smoke would follow the path of least resistance and would billow outwardly through the open access door. In order to prevent this, the co-pending Schwartz application discloses damper means which must be moved to an open or non-blocking position before the access door of the stove can be opened, thus insuring that the combustion gases and smoke will be exhausted through the flue, rather than being forced into the room through the open access door. The present invention uses this same basic type of damper system, but the present invention utilizes novel and unique means for preventing excess smoke spillage into the room should the catalytic converter become blocked or clogged for any reason. In the aforesaid co-pending Schwartz application, this problem was overcome by the provision of controlled leakage means which permitted combustion gases to exit through the flue in those situations where the damper was in closed position and the converter became clogged or blocked for some reason. In the present invention no such controlled leakage need be provided since it has been found that if all of the draft means in the stove are located below the fuel support level in the stove, then where a blockage occurs, the combustion gases will move downwardly within the stove to the level of the draft means, whereby the gases will actually smother the fire before significant amounts of gases can be forced out through the draft inlets, whereby minimal pollutants will exit from the stove. Thus, an important feature of the present invention is the provision of a wood burning stove wherein all draft control means are located below the fuel support level within the stove, and this applies not only to primary air draft controls, but also secondary air draft controls, etc.
Another important feature of the present invention resides in the fact that it has been found highly desirable to introduce secondary air to the stove at a location adjacent that of the catalytic converter. Specifically, sensing means are provided adjacent the converter which function to sense the presence of unburned hydrocarbons or oxygen in the flue gases after passage through the converter whereby if sufficient combustion is not taking place, a supply of secondary air will be automatically introduced to insure proper air/fuel ratio and hence promote more complete combustion. As previously indicated, even though the secondary air is introduced at a location adjacent the converter which in turn is located above the primary combustion chamber, the draft control means for the secondary air is located below the fuel support level in the primary combustion chamber. Another important feature is the fact the the primary and secondary air supplies and controls are completely separate and independent of each other. Thus, introduction of secondary air to the converter in no way affects the primary air in the firebox.
It is has also been found desirable in the present invention to utilize sequential converters, i.e., a first converter located at the top of the firebox and a second converter in registry therewith and spaced thereabove. The use of sequential converters promotes more complete combustion and hence great overall efficiency.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.